A normal PN junction diode is used for unidirectional flow of charge current. The output of the solar panel depends on the intensity of the solar light. To regulate this voltage, LM317 is used. LM317 is an adjustable voltage regulator. The regulator circuit is designed to get a fixed voltage of 5V.
An alternative charger circuit is also provided to charge the mobile by house hold general purpose 230V in the absence of the sun light. This charge circuit uses regulated 5V, 750mA power supply. 7805 three terminal voltage regulator is used for voltage regulation. Bridge type full wave rectifier is used to rectify the ac output of secondary of 230/18V step down transformer.